The invention relates to improvements in slip fit or so-called "stab" type coupling joints for smooth wall tubing, and more particularly to a threadless coupling which can be rapidly connected to smooth wall piping or tubing for fluid distribution systems such as gas and water.
Pipe couplings of various types are well known in the prior art. Many of the prior art type couplings require the ends of the pipe or tubing to be threaded, flanged, flared, belled or otherwise pre-treated, deformed or specially formed. Such couplings have not been totally satisfactory since the special formation or treatment is time consuming and costly and most objectionably makes assembly or installation in the field difficult. Design of the threadless couplings is to some extent controlled by the type of pipe or tubing with which the joint is to be used. For example, some prior art type coupling joints employ so-called "Chinese" fingers. Others use a compression coupling approach which utilize gripper rings, both solid and split, but have lacked flexibility in the design of their component parts. In addition, the split gripper rings have to be cammed to contract about the pipe in order to grip when an outward load is applied. A principle problem has been in designing a threadless coupling having acceptable pull-out resistance, installation load and initial and final grip specifications. Other prior art designs have utilized "belleville" springs which are frusto-conical locking rings which have to be flattened to a planar condition to reduce the interior diameter of the same to grip the tubing. In other configurations, gripper washers, whether solid or split, and having radially inwardly extending teeth have been used but in these types design of the joint and manufacture of the same is complicated. Furthermore, the prior art devices do not allow for rotation of the tubing. Thus, complexity of design resulting in manufacturing and field installation difficulties have been continuing problems. The prior art devices simply have not provided sufficient tensile strength for particular purposes such as for couplings of cast iron or steel, nor are they easily produced in variable or high constant tensile strength configurations. They are difficult to remove from coupled pipes, and have not had effective sealing when utilized with a section of pipe or tubing having an out-of-round condition on the outer surface or if scratches or marring of the tube surface were present.
Among the prior art patents considered with respect to this invention are the following U.S. Pat. Nos.: 1,817,776; 2,491,004; 3,645,567; 3,924,877; 3,924,882; 3,995,897; 4,062,574; and 4,073,514, all of which are considered to be of interest only.